Table 1 Characteristics of the ALSPAC-enrolled sample and complete cases

Enrolled singletons and twins, alive at 1 year and not withdrawn from the study (n = 14,665)1

Complete cases (n = 1869)

Sex

Male
Female

7524 (51%)
7141 (49%)

802 (43%)
1067 (57%)

Maternal age

< 25
25–29
30+

3336 (24%)
5394 (39%)
5224 (37%)

173 (9%)
694 (37%)
1002 (54%)

Mother’s education2

CSE/vocational
O level
A level
Degree/higher

3723 (30%)
4287 (35%)
2786 (22%)
1599 (13%)

237 (13%)
620 (33%)
570 (31%)
442 (24%)

Family occupational social3 class

Non-manual
Manual

9254 (81%)
2231 (19%)

1698 (91%)
171 (9%)

Maternal anxiety

No
Yes

4808 (51%)
4584 (49%)

1158 (62%)
711 (38%)

Biological father lives with child (age 4)

No
Yes

1217 (13%)
8270 (87%)

123 (7%)
1746 (93%)

Parental conflict

No
Yes

10,008 (88%)
1305 (12%)

1719 (92%)
150 (8%)

Child bullied since age 12 (at age 16)

No
Yes

4175 (83%)
885 (18%)

1549 (83%)
320 (17%)

Child IQ (age 8)

Mean (SD)

104 (17)5

110 (15)

Maternal depression (EPDS)4

Mean (SD)

5 (5)6

5 (4)

Number living in home

Median (IQR)

4 (4–5)7

4 (4–4)

Early family TV use score

Mean (SD)

4 (2)8

3 (2)

TV, weekdays

None/< 1 h
1–2 h
3+ hours

1306 (26%)
2648 (52%)
1118 (22%)

475 (25%)
1030 (55%)
364 (19%)

Texting, weekdays

None/< 1 h
1–2 h
3+ hours

2990 (59%)
1177 (23%)
898 (18%)

1199 (64%)
404 (22%)
266 (14%)

Computer use, weekdays

None/< 1 h
1–2 h
3+ hours

1171 (23%)
2416 (48%)
1481 (29%)

421 (23%)
928 (50%)
520 (28%)

TV, weekends

None/< 1 h
1–2 h
3+ hours

1015 (21%)
2270 (46%)
1615 (33%)

359 (19%)
914 (49%)
596 (32%)

Texting, weekends

None/< 1 h
1–2 h
3+ hours

2689 (55%)
1188 (24%)
1024 (21%)

1104 (59%)
436 (23%)
329 (18%)

Computer use, weekends

None/< 1 h
1–2 h
3+ hours

1108 (23%)
1950 (40%)
1843 (38%)

388 (21%)
770 (41%)
711 (38%)

Anxiety

No
Symptoms
Diagnosis

2410 (53%)
1630 (36%)
522 (11%)

1000 (54%)
686 (37%)
183 (10%)

Depression

No
Symptoms
Diagnosis

2736 (60%)
1466 (32%)
360 (8%)

1143 (61%)
598 (32%)
128 (7%)

1Denominators vary because the variables come from different questionnaires and have different completion rates.

2CSEs (Certificate of Secondary Education)/ and O levels were qualifications taken at age 16 – now replaced by GCSEs (General Certificate of Secondary Education) in England, Wales and Northern Ireland. A levels are exams taken at age 18 in these countries.

3Family occupational social class was based on the higher of the mother or partner’s occupational social class using the 1991 British Office of Population and Census Statistics (OPCS) classification and was dichotomized into non-manual (professional, managerial or skilled professions) and manual (partly or unskilled occupations).